A newly discovered chemical weapon in poison frogs’ arsenal

Scientists have discovered new toxins that some Amazonian poison frogs use as a chemical defense against predators.
Credit: The American Chemical Society

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New
research documents a surprising chemical weapon used by some Amazonian
poison frogs. The study identified for the first time a family of
poisons never before known to exist in these brightly colored creatures
or elsewhere in nature: the N-methyldecahydroquinolines. The authors
then speculated on its origin in the frogs’ diet, most likely ants. The
report is scheduled for the June 26 issue of ACS’ Journal of Natural Products, a monthly publication.

H. Martin Garraffo and colleagues note there are more than 500
alkaloids, potentially toxic substances, known to exist in the skin of
poison frogs of the family Dendrobatidae. Frogs use them as a chemical
defense to discourage predators from biting and eating them. Western
Colombian natives have used skin extracts from another group of frogs,
unrelated to those in the new study, to coat blow-darts for hunting.

Frogs
get nearly all of the alkaloids from their diet, removing alkaloids
from ants, mites, small beetles, millipedes and possibly other small
arthropods, concentrating them with incredible efficiency, and storing
them in their skin. However, Garraffo’s group was not certain about the
origin of the newly discovered N-methyldecahydroquinolines, which could
also be produced in the frogs’ own bodies. Feeding experiments with
alkaloids fed to captive frogs are planned, which might settle this
point.

The scientists analyzed alkaloids from the skin of 13 of the more than
25 species of the genus Ameerega of poison frogs. They identified the
new toxins in the frogs as being of the N-methyldecahydroquinoline
class, which were present among several other alkaloids.